Nanocomposite ceramics of oxide and no-oxide phases and methods for producing same

ABSTRACT

A composite of nanoscale oxide ceramic phases is dispersed in a non-oxide ceramic matrix material. The non-oxide ceramic phase may be silicon-carbon-nitrogen-based, and imparts resistance to mechanical degradation, resistance to chemical degradation, and resistance to oxidation at temperatures up to 1800° C. The nanodispersed oxide phase is selected according to desired functional properties, including coefficient of thermal expansion, rheology, ferromagnetic and superparamagnetic properties, superdielectric properties, and superpiezolectric and electrostrictive properties. A method is provided for making a nanocomposite ceramic fiber having a nanodispersion of zirconia in a silicon-carbon-nitrogen ceramic phase. A method is provided for making a soft ferromagnetic ceramic having a nanodispersion of ferrite in a zirconia in a silicon-carbon-nitrogen ceramic phase.

This invention was made with Government support. The Government hascertain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention involves methods and materials for ceramics and,more particularly, methods and materials for amorphous nanocompositeceramics and devices utilizing the same.

2. Statement of the Problem

Formation of ceramics from polymer precursors has received widespreadattention recently, mainly because the processing is done at lowertemperatures and with simpler procedures than conventional processes ofsintering ceramic powders.

The formation of ceramics from polymer precursors is typically performedby first thermosetting the polymer precursor to a solid material, andthen pyrolyzing the solid material to form the ceramic.

One of the most interesting groups of such ceramic materials includesamorphous compounds of silicon, carbon, and nitrogen. Amorphous siliconcarbonitride (SiCN) is a relatively new material with potential for awide range of applications requiring materials with multifunctionalproperties. This potential is due to SiCN being chemically stable attemperatures up to 1500° C., and having excellent resistance to creep,oxidation, and thermal shock. Bulk form SiCN has been fabricated fromcommercially available polymeric precursors. There are significantshortcomings, however, with present SiCN fabrication methods that havelimited its use and prevented many products from being commerciallysuccessful. One major reason for this lack of success lies in the natureof the current process used to make polymer-based SiCN materials.

The current process for making polymer-based SiCN materials consists oftwo steps: thermosetting, which is typically polymerization of a liquidform of the precursor into a rigid plastic body, known as the “greenbody”, followed by pyrolyzing the rigid plastic into a monolithic SiCNceramic. These SiCN ceramics are a non-oxide ceramic, as oxygen has beenconsidered generally to be detrimental to the material.

There are shortcomings with the monolithic SiCN ceramics of the priorart. One is that, being non-oxide, they lack functional properties ofexisting oxide ceramic monolithic components such as magnets,capacitors, ferroelectric actuators, and others. For this reason, theexisting SiCN monolithic ceramics, although having superior mechanicaland thermo-mechanical properties over oxide monolithic ceramics, arefrequently not suitable replacements.

Another problem with the present process for making polymer-based SiCNmaterials is the respective temperatures at which thermosetting beginsand pyrolysis begins, coupled with the rheology of the known precursors.This substantially limits the scope of shapes, forms, and applicationsof the SiCN products.

One example of this limitation is apparent from the ongoing quest forSiCN fiber. The search for SiCN fiber is not new, as it has been known,in theory anyway, that such fiber could replace graphite fiber for manyapplications with increased scope of use and improvement in performance.The reason is that graphite exhibits oxidation, devitrification, anddegradation above about 800° C. in air. SiCN is stable at considerablyhigher temperatures. The difficulty, though, is that acceptable qualityfibers of SiCN ceramic are difficult to economically produce using thecurrent methods. The fabrication is difficult because, ideally, theprecursor would have a rheology suitable for fiber drawing at atemperature just below the thermosetting temperature, and that it havean onset of pyrolysis at a temperature just above the thermosettingtemperature. This would allow the fiber to be drawn and immediatelythereafter thermoset into a rigid form, which could then be pyrolyzedwithout losing its shape. Known precursors of SiCN, however, do not havethese qualities.

Others have attempted SiCN-type fibers, or alternates, as part of thisquest to replace graphite. In the mid-1990s, the Bayer company inGermany announced it had a process for drawing fibers from silicon boroncarbonitride (SiBCN); however, this process is known in the art to betoo expensive and has not evolved into a successful commercial venture.Nicalon has been used, but Nicalon fibers devitrify at about 1100° C. to1300° C.

SOLUTION

The present invention advances the art and overcomes the aforementionedproblems by a composite of nanoscale oxide ceramic phases dispersed in anon-oxide ceramic matrix material. The composite achieves new synergiesin the properties of the composite, not only combining the properties ofthe oxide and non-oxide materials into one composite material, but alsoproviding a new genre of materials where the nanoscale dispersion of theoxide phase leads to novel properties that cannot be obtained in thecoarser microstructure of the monolithic oxide materials. In a preferredembodiment, the non-oxide ceramic is silicon-carbon-nitrogen-based andthe matrix of this phase imparts resistance to mechanical degradation,resistance to chemical degradation, and resistance to oxidation attemperatures up to 1800° C. The nanodispersed oxide phase imparts other“functional” properties, in addition to the high temperature propertiesof the matrix, to the composite, including: (a) tailored coefficient ofthermal expansion; (b) superparamagnetic properties up to very hightemperatures; (c) super ferromagnetic properties; (d) superdielectricproperties; and (e) superpiezolectric and electrostrictive properties,etc. The term “super” is applied to these composites for two reasons:(i) because the composites have mechanical and chemical durability athigh temperatures, which cannot be sustained in the monolithic oxidematerials; and (ii) because the nanoscale dispersion of the oxide phaseoften leads to novel functional behavior that is not obtained inmicroscale, monolithic, polycrystalline oxide materials.

The dispersion of the functional oxide ceramics in an amorphousnon-oxide matrix of silicon carbon and nitrogen is readily obtained viathe methods of this invention, and provides functional as well asmechanical properties superior to, and additional to, those found intheir monolithic counterparts. These nanocomposites can replacefunctional oxide ceramic monolithic components such as magnets,capacitors, ferroelectric actuators, and others. Industries includingmechanical, electrical, electronic, telecommunication, aerospace, andothers will find wide applicability of this invention. This inventionis, therefore, a paradigm shift for the functional ceramic monoliths.

One embodiment of the invention includes a nanoscale dispersion ofpredominantly crystalline oxide phases in a predominantly amorphousmatrix of a non-oxide ceramic phase. In the preferred embodiment, thenon-oxide ceramic phase is composed primarily of the elements silicon,carbon, and nitrogen, but may contain other dopants, such as boron, inorder to control the properties of the matrix phase. The phrase“silicon-carbon-nitrogen based material” is defined herein as apredominantly amorphous matrix of a non-oxide ceramic phase, composedprimarily of the elements silicon, carbon, and nitrogen, but which maycontain other dopants.

The dispersed oxide phase includes, but is not limited to, zirconia,alumina, spinels (e.g., nickel iron oxides), oxides of iron, perovskites(e.g., barium titanate), ceramics with piezoelectric properties (e.g.,PZT), dielectric materials (e.g., barium strontium titanate), otherperovskites, sometimes referred to as ABO₃-type materials, and any othersuitable oxide ceramics.

Another embodiment of the invention includes a material containing ananodispersion of zirconia in a SiCN matrix. The matrix phase impartsresistance to mechanical deformation, resistance to oxidation, andresistance to chemical degradation at temperatures up to 1800° C.

In the preferred embodiment, the polymeric precursor materials includesilanes, silazanes, and polysilazanes which result in SiCN ceramics uponcrosslinking and pyrolysis. The composition of the ceramic product canbe varied by appropriate selection of the polymeric precursor materialand the pyrolysis environment, and to a lesser extent, by appropriateselection of the casting conditions. One suitable polysilazane isCeraset™, manufactured and distributed by Kion Corporation, Columbus,Ohio. In accordance with the present invention, the crosslinking can beaccomplished by any suitable polymerization reaction known in the artthat yields the desired crosslinked polymeric structure. Pyrolysis underargon or nitrogen at temperatures typically less than approximately1400° C. results in SiC_(x)N_(y), where x and y can be varied using amixture of ammonia and argon.

Another embodiment of the invention includes a fiber formed of thenanodispersion of zirconia in a SiCN matrix. The zirconia phase allowsdrawing fibers from a commercial source of the polymer that is used inthe fabrication of SiCN, such as Ceraset™. These fibers have a farsuperior chemical stability at high temperatures as compared topresently available non-oxide fibers, collectively known as Nicalonfibers.

Still another embodiment of the invention includes a nanodispersion ofiron oxide in a SiCN matrix, which exhibits remarkable magneticproperties, and superparamagnetic behavior, normally not seen inmonolithic ferromagnetic oxide-based ceramics. One aspect of thisembodiment is the polymer-derived SiCN matrix having chemical stabilityat elevated temperatures and excellent resistance to creep, oxidation,and thermal shock. Ferromagnetic ceramics like Fe₂O₃ and Fe₃O₄ have poormechanical strength, high coercivity, and high hysterisis loss.

A further aspect of the invention includes a nanocomposite ceramichaving a tailored coefficient of thermal expansion. The nanocompositemay be a nanodispersion of zirconia in a SiCN matrix. The coefficient ofthermal expansion of SiCN is tailored by the incorporation of 1 weightpercent to 99 weight percent zirconium oxide. Yet another aspect of theinvention is a sealing material for multilayer fuel cell structures athigh temperature, comprising a nanocomposite ceramic having a tailoredcoefficient of thermal expansion. The nanocomposite may be ananodispersion of zirconia in a SiCN matrix.

Another aspect of the invention is a nanodispersion ofbarium-strontium-titanate in a SiCN matrix, which has superdielectricproperties as well as superior mechanical structure and thermalstability.

Numerous other features, objects and advantages of the invention willbecome apparent from the following description when read in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photomicrograph of a nanocomposite Si—C—N—Zr—O fiberspecimen obtained via a method of the present invention;

FIG. 2 is a graph comparing the oxidation resistance of a nanocompositeSi—C—N—Zr—O fiber via a method of the present invention with that of apure SiCN fiber, each obtained via a method of the present invention;

FIG. 3 is a graph comparing the thermal stability of the Si—C—N—Zr—Ofiber prepared via a method of the present invention with that of acommercially available Nicalon fiber (Nicalon NL202);

FIG. 4 is a photomicrograph of a Si—C—N—Zr—O fiber specimen obtained viaa method of the present invention; and

FIG. 5 is a graph comparing the hysterisis curve of a prior art ferritemagnetic material with that of an amorphous nanocomposite Si—C—N—Fe—Omagnetic material specimen obtained via a method of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a photomicrograph of a nanocomposite Si—C—N—Zr—O fiberspecimen, comprising a nanodispersion of zirconia in a SiCN matrix,obtained via the following described method of the present invention.The specimen was produced from commercially available Ceraset™ andzirconium propoxide (Zr-n-p) dissolved in propanol. They are the sourcesof SiCN and ZrO₂, respectively. The yield of SiCN and ZrO₂ from Ceraset™and Zr-n-p solution, after pyrolyzing at 1000° C. in N₂, was measured tobe 78% and 28% weight percentage respectively. Based on this yield,Ceraset and Zr-n-p solution were taken in appropriate proportion so asto get 10% volume percentage of ZrO₂ in the fiber after pyrolysis at1000° C. in N₂. First, the Ceraset™ and the Zr-n-p solution were mixedtogether and heat treated at 160° C. to yield viscous liquid. The fiberwas then drawn from this viscous liquid at room temperature. The fiberthen was thermosetto a rigid solid above 160° C. and pyrolyzed at 1000°C.

The SiCN matrix phase of the Si—C—N—Zr—O fiber of the invention impartsresistance to mechanical deformation, resistance to oxidation, andresistance to chemical degradation at temperatures up to 1800° C. Theinvention's addition of the zirconia phase changed the rheology of theSiCN precursor to enable drawing of fibers from Ceraset™ and othercommercially available sources of the polymer used in the fabrication ofSiCN. Otherwise, the fiber drawing from these commercially availableprecursors is not possible.

As can be seen from the FIG. 1 photomicrograph, the surface of thespecimen Si—C—N—Zr—O fiber is dense and free from defects. X-raydiffraction confirmed both the SiCN and ZrO₂ as being in an amorphousphase. The fracture strength and Young's modulus of Si—C—N—Zr—O fiberwere evaluated to be 2.6 GPa and 160 GPa respectively, with a fiberdiameter of 11 μm. As a comparison, the highest reported fracturestrength of SiCN fiber from laboratory derived precursor is 2.5 GPa,with a fiber processing involving expensive y-ray curing.

FIG. 2 is a graph comparing the oxidation resistance of pure SiCN with ananocomposite Si—C—N—Zr—O fiber of the invention, formed of SiCN with ananodispersion of 10% ZrO₂ by volume. As seen in the FIG. 2 graph, theSi—C—N—Zr—O fiber has significantly better oxidation resistance thanSICN alone. Accordingly, the Si—C—N—Zr—O fiber formed by the invention,using the readily prepared modified precursor, possesses both excellentand superior fracture strength and oxidation resistance compared to SiCNfiber.

FIG. 3 is a graph comparing the thermal stability of the Si—C—N—Zr—Ofiber of the invention with that of a commercially available Nicalonfiber (Nicalon NL202). The experiment was carried out under identicalconditions for both cases. Under these identical experimentalconditions, initiation of thermal degradation for commercially availableNicalon fiber starts at 1300° C. On the other hand, Si—C—N—Zr—O fiber isstable up to approximately 1500° C. Moreover, the weight loss at 1600°C. is only 5% for S—C—N—Zr—O fiber, while that for Nicalon fiber isobserved to be approximately 20%. Thus, the present invention'sSi—C—N—Zr—O fibers have a far superior chemical stability at hightemperatures as compared to presently available non-oxide fibers such asNicalon fibers.

FIG. 4 is a photomicrograph of another SiCN—ZrO₂ fiber specimen obtainedvia the present invention. The specimen shown in FIG. 4 was pyrolyzed at1300° C. The surface shows uniform dispersion of nanoparticles of ZrO₂in a SiCN matrix.

The Si—C—N—Zr—O fiber of the present invention is contemplated to havesignificantly improved performance and a much wider scope ofapplications compared to the currently used graphite and/or Nicalonfibers. The contemplated applications include those involving extremeenvironments of temperature and/or chemical reactants, including thosecausing oxidation. These are important because graphite and Nicalontypically suffer from oxidation, devitrification and degradation in suchenvironments. Graphite oxidizes (burns) above about 800° C. in air,while Nicalon fibers degrade by devitrification at about 1100° C. to1300° C. The Si—C—N—Zr—O fibers of the invention are stable attemperatures up to 1500° C. in an air environment.

Particular contemplated applications of Si—C—N—Zr—O fibers of thepresent invention include materials for brakes in aircraft, where thecurrent practice is to use graphite fibers, heat exchangers in energyconversion systems, and applications in space technologies. Anotherembodiment of the invention is an amorphous nanocomposite Si—C—N—Fe—Osoft ferrite magnetic material. FIG. 5 is a graph illustrating one ofthe benefits of this material. The graph of FIG. 5 plots inducedmagnetization in Gauss as function of applied field in Oesterds. Theinset shows the same graph for a prior art material, Fe₃O₄, and aclearly drastic improvement in a sample's hysterisis loss when comparedto a sample of the prior art ferrite magnetic material.

The FIG. 5 sample composite was made by a polymer derived route usingpowdered Fe₃O₄ obtained from Fisher Scientific, Fair Lawn, N.J., andCeraset™, obtained from Kion Corporation, Columbus, Ohio. The powderedFe₃O₄ was dispersed in liquid Ceraset™ using an ultrasonic bath. Thedispersion was heat treated at 400° C. in a nitrogen environment tocrosslink the precursor mixture. The heat treated composition was ballmilled, followed by pelletization by warm pressing at 350° C. and 30MPa. The pellet was then pyrolyzed under a flowing nitrogen environmentat 1000° C., with very slow heating and cooling rates. The mixing ratioof powdered Fe₃O₄ to liquid Ceraset™ was such that the final pyrolyzedceramic composition was Fe₃O₄-70% and SiCN-30% by volume in finalcomposite.

As seen from the FIG. 5 “Magnetization vs. Applied Field” curve, theamorphous nanocomposite SiCN—Fe₃O₄ of this invention has near zerohysterisis. Further, the FIG. 5 curve for the ferrite shows a coerciveforce of about 1000 Oesterds, while the nanocomposite exhibits acoercive force of only 10 Oesterds.

The nanocomposite of SiCN and ferrite of this invention has remarkableproperties which have never before been seen in monolithic ferrites,including: (a) ten to two hundred times the permeability of monolithicpolycrystalline ferrites; and (b) nearly zero coercive field andnegligible hysteretic loss.

Further, the SiCN—Fe₃O₄ composite can be fabricated by this invention atlow temperatures such as, for example, less than 1000° C. In comparison,monolithic ferrites are prepared by the sintering process at much highertemperatures (1200° C. to 1400° C.). The sintering process often employssintering aids that can degrade the properties of the material. Thepolymer derived process of the invention does not involve any sinteringaids.

Still further, the polymer-derived SiCN matrix of this embodiment haschemical stability at elevated temperatures and excellent resistance tocreep, oxidation, and thermal shock. Ferromagnetic ceramics, like Fe₂O₃and Fe₃O₄, have poor mechanical strength. The fracture strength ofSiCN—Fe₃O₄ nanocomposites was measured to be 175 MPa. This compositedoes not exhibit any degradation in magnetic properties when in use at atemperature of approximately 500 C in air. Therefore, the SiCN—Fe₃O₄nanocomposite of this invention has these benefits in addition to itsclearly superior coercivity and hysterisis characteristics.

The soft ferrite nanocomposite SiCN and ferrite materials produced bythe methods of this invention are contemplated to have extensiveapplications including, for example, without deflection yokes of cathoderay tubes (CRT), power switch transformers, retro-sweeping transformerfor televisions, radio antennae, chokes, rotary transformers of audiovisual (AV) machines, ballast of energy saving lights, and transformers.

A further aspect of the invention is attained by using zirconium oxideas the oxide phase of the oxide/non-oxide nanodispersion ceramic of theinvention. Zirconium oxide provides selective tailoring of thecoefficient of thermal expansion of the SiCN matrix, ranging from 1weight percent to 99 weight percent zirconium oxide. A contemplatedproduct of zirconium oxide as the oxide phase nanodispersed in thenon-oxide SICN is a sealing material for multilayer fuel cellstructures, usable at high temperatures.

Another aspect of the invention is a nanodispersion ofbarium-strontium-titanate in a SiCN matrix, which is predicted by thepresent inventors as likely having superdielectric properties as well assuperior mechanical structure and thermal stability.

Particular contemplated applications of the Si—C—N—Zr—O system alsoinclude multilayer coating systems in high temperature components suchas blades, combustors, nozzles, and linings in gas turbine engines. Thepolymer route to processing and the nanoscale microstructure of thesecoatings can be an advantage in providing thermal and environmentalbarriers for higher performance in high temperature and aggressiveenvironments.

Each of the above examples shows a different and novel aspect of thecomposite materials according to the present invention. The scope ofthis invention, however, is not limited to these examples but extendsgenerally to composites that are constructed from the SiCN-basednon-oxide matrix, and the broad range of oxide ceramics described above.The present invention advances the art by dispersing crystalline oxideceramics at nanometer scale in noncrystalline, non-oxide ceramics toimpart various functional properties to the composite. The functionalproperties exhibited by the composite far exceed those predictable, withany reasonable degree of certainty, by a simple rule of mixtures forcomposites. These composites, according to the invention, exhibit bettermechanical properties than their monolithic counterparts. Further, theinvention's methods of dispersing functional oxide ceramics in anamorphous non-oxide matrix are readily carried out.

It should be understood that the particular embodiments shown in thedrawings and described within this specification are for purposes ofexample and should not be construed to limit the invention which will bedescribed in the claims below.

1. a ceramic nanocomposite, comprising: a substantially amorphous matrixof non-oxide ceramic phase; and a nanoscale dispersion of crystallineoxide phases in said substantially amorphous matrix.
 2. A ceramicnanocomposite according to claim 1 wherein said non-oxide ceramic phaseincludes a silicon atom, a carbon atom, and a nitrogen atom.
 3. Aceramic nanocomposite according to any of claim 1 wherein saidcrystalline oxide phases include crystalline oxide phases from the groupconsisting of zirconia, alumina, spinels, and oxides of iron.
 4. Aceramic nanocomposite according to any of claim 1 wherein saidcrystalline oxide phases include a perovskite.
 5. A ceramicnanocomposite according to any of claim 1 wherein said crystalline oxidephases include a piezoelectric material.
 6. A ceramic nanocompositeaccording to any of claim 1 wherein said crystalline oxide phasesinclude a dielectric material.
 7. A method for producing a nanocompositeceramic fiber, comprising steps of: providing a primary precursor, saidprimary precursor being a precursor of a non-oxide ceramic; mixing asecondary precursor with said primary precursor to form an intermediatemixture, said secondary precursor being a precursor of an oxide ceramic;heating said intermediate mixture to a viscous state; drawing saidviscous intermediate mixture into a fiber; thermosetting said fiber intoa rigid state; and pyrolyzing said fiber to form a nanocomposite fibercomprising a nanophase distribution of said oxide ceramic within saidnon-oxide ceramic.
 8. A method as in claim 7 wherein said thermosettingis performed at a temperature above 160° C.
 9. A method for producing ananocomposite fiber according to claim 7 wherein said oxide ceramic is ametal oxide ceramic and said secondary precursor is an organo-metallicprecursor of said metal oxide ceramic.
 10. A method for producing ananocomposite fiber according to claim 7 wherein said non-oxide ceramiccontains a silicon atom, a carbon atom, and a nitrogen atom.
 11. Amethod for producing a nanocomposite fiber according to claim 7 whereinsaid oxide ceramic contains atoms selected from groups III and IV of theperiodic system of the elements or transition metals or lanthanoidmetals and oxygen.
 12. A method for producing a nanocomposite fiberaccording to claim 7 wherein said oxide ceramic contains a zirconiumatom and an oxygen atom.
 13. A method for producing a nanocompositefiber according to claim 7 wherein said primary precursor does not haveany temperature to make it viscous for drawing fiber, has a firstthermosetting temperature, and has a first pyrolyzing temperature, andwherein said secondary precursor has a first drawing temperature to makeit viscous for fiber drawing, has a second thermosetting temperature,and has a second pyrolyzing temperature; wherein a mixture of saidprimary and secondary precursors has a second drawing temperature tomake it viscous for drawing fiber, has a third thermosetting temperatureclose to said second drawing temperature, and a third pyrolyzingtemperature.
 14. A nanocomposite ceramic fiber, comprising: a non-oxideceramic; and a nanophase distribution of an oxide ceramic within saidnon-oxide ceramic.
 15. A nanocomposite ceramic fiber according to claim14 wherein said non-oxide ceramic is amorphous.
 16. A nanocompositeceramic fiber according to claim 14 wherein said oxide ceramic isamorphous.
 17. A nanocomposite ceramic fiber according to claim 14wherein said non-oxide ceramic contains a silicon atom, a carbon atom,and a nitrogen atom.
 18. A nanocomposite ceramic fiber according toclaim 14 wherein said oxide ceramic contains atoms selected from groupsIII and IV of the periodic system of the elements or transition metalsor lanthanoid metals and oxygen.
 19. A nanocomposite ceramic fiberaccording to claim 14 wherein said oxide ceramic contains a zirconiumatom and an oxygen atom.
 20. A method for making a ceramic nanocompositemagnet, comprising steps of: mixing a ferrite powder in a polymericprecursor of silicon carbonitride to obtain a liquid precursordispersion mixture; crosslinking said liquid precursor dispersionmixture into an interim solid body; powdering said interim solid bodyinto an interim powder; pelletizing said interim powder into an interimpellet; and pyrolyzing said interim pellet into a nanocomposite ofsilicon carbonitride and ferrite.
 21. A method for making a ceramicnanocomposite magnet according to claim 20 wherein said mixing iscarried out with an ultrasonic bath.
 22. A method for making a ceramicnanocomposite magnet according to claim 20 wherein said crosslinkingstep includes heating said liquid precursor dispersion mixture to atleast approximately 400° C.
 23. A method for making a ceramicnanocomposite magnet according to claim 21 wherein said crosslinkingstep includes heating said liquid precursor dispersion mixture to atleast approximately 400° C.
 24. A method for making a ceramicnanocomposite magnet according to claim 20 wherein said pelletizing stepincludes heating and compressing said interim powder in a pellet-shapedmold mixing.
 25. A method for making a ceramic nanocomposite magnetaccording to claim 20 wherein said mixing step mixes said liquidprecursor dispersion mixture to have a nanocomposite composition ofapproximately 70% ferrite and 30% silicon carbonitride, by volume.
 26. Amethod for making a ceramic nanocomposite magnet according to claim 20wherein said mixing comprises mixing said liquid precursor dispersionmixture to have a nanocomposite composition of substantially 70% ferriteand 30% silicon carbonitride, by volume.
 27. A method for making aceramic nanocomposite magnet according to claim 20 wherein said mixingstep mixes said ferrite powder and polymeric precursor of siliconcarbonitride in a ratio such that said nanocomposite of siliconcarbonitride and ferrite has a coercivity approximately two orders ofmagnitude less than a coercivity of a ferrite magnetic material.
 28. Amethod for making a ceramic nanocomposite magnet according to claim 20wherein said mixing comprises mixing said ferrite powder and polymericprecursor of silicon carbonitride in a ratio such that saidnanocomposite of silicon carbonitride and ferrite has a coercivitysubstantially two orders of magnitude less than a coercivity of aferrite magnetic material.
 29. A method for making a ceramicnanocomposite magnet according to claim 20 wherein said crosslinkingstep includes heating said liquid precursor dispersion mixture to atleast approximately 400° C. in a nitrogen atmosphere.
 30. A method formaking a ceramic nanocomposite magnet according to claim 20 wherein saidcrosslinking includes heating said liquid precursor dispersion mixtureto at least approximately 400° C. in a nitrogen atmosphere.
 31. A methodfor making a ceramic nanocomposite magnet according to claim 20 whereinsaid pyrolyzing includes heating said pellet to a temperature ofapproximately 1000° C.
 32. A method for making a ceramic having apredetermined coefficient of thermal expansion, said method comprising:providing a primary precursor, said primary precursor being a precursorof a non-oxide ceramic having a first coefficient of thermal expansion;mixing a secondary precursor with said primary precursor to form anintermediate mixture, said secondary precursor being a precursor of anoxide ceramic having a second coefficient of thermal expansion;thermosetting intermediate mixture into an intermediate material; andpyrolyzing said intermediate material to form a nanocomposite ceramiccomprising a nanophase distribution of said oxide ceramic within saidnon-oxide ceramic, wherein said mixing comprises mixing said secondaryprecursor and said primary precursor in a ratio such that saidnanocomposite ceramic has said predetermined coefficient of thermalexpansion.
 33. A method for making a ceramic having a predeterminedcoefficient of thermal expansion according to claim 32 wherein saidoxide ceramic includes a zirconium atom.
 34. A method as in claim 32 andfurther including: providing a substrate; prior to said step ofpyrolyzing, applying said intermediate mixture or said intermediatematerial to said substrate; and wherein said mixing comprises mixingsaid secondary precursor and said primary precursor in a ratio such thatsaid nanocomposite ceramic has a coefficient of thermal expansionmatched to said substrate.
 35. A method as in claim 34 wherein saidcoefficient of thermal expansion is matched to said substrate attemperatures of 500° C. or higher.
 36. A method as in claim 34 whereinsaid substrate comprises a metallic or ceramic material.
 37. A method asin claim 34 wherein said providing, mixing, applying, thermosetting, andpyrolyzing are repeated to provide a graded nanocomposite ceramiccoating.
 38. A ceramic coated structure, comprising: a substrate; and aceramic nanocomposite coating comprising a crystalline oxide ceramic ina substantially non-oxide ceramic, said coating having a coefficient ofthermal expansion to match said substrate.
 39. The structure of claim 38wherein said substrate is either metallic or ceramic.
 40. The structureof claim 38 wherein said coating is a multilayer graded coating in whicheach layer has a different proportion of said crystalline oxide ceramicto said non-oxide ceramic.
 41. The structure of claim 38 wherein saidcoating imparts resistance to corrosion at high temperatures.
 42. Aceramic nanocomposite according to claim 2 wherein said crystallineoxide phases include crystalline oxide phases from the group consistingof zirconia, alumina, spinels, and oxides of iron.
 43. A ceramicnanocomposite according to claim 2 wherein said crystalline oxide phasesinclude a perovskite.
 44. A ceramic nanocomposite according to claim 2wherein said crystalline oxide phases include a piezoelectric material.45. A ceramic nanocomposite according to claim 2 wherein saidcrystalline oxide phases include a dielectric material.